In a food processor, combine the walnuts, almond flour, dates, coconut oil, cardamom and salt. Pulse until the mixture begins to come together and you can easily pinch it between your fingertips. Press the crust mixture into a 9-inch tart pan, pressing it evenly into the base and up the sides. In a high-speed blender, combine the cashews, coconut cream, lemon juice, and salt, and blend until airy and smooth. Pour the filling into the crust and chill the entire tart for at least 1 hour. Just before serving, top with berries or sliced fruit.
